I'm getting these weird spots on my Mechanical arm?
Those spots are due to the voronoi that is feeding your leftmost principled's roughness.  You're getting random-ish circles from that texture that your color ramp is then quantizing into 0 or 1.  If you don't want it to look like that, don't do that to its roughness.  (The normal of the leftmost principled is also a function of that voronoi, so you probably want to change that as well, but it's subtle, whereas your roughness is anything but.)
While it's not responsible for the problems shown, what you're doing with the normal input on your rightmost principled also doesn't make any sense.  A &quot;normal&quot; output is a (world space) vector-- 3 components.  Do not feed it into a math node or a colorramp or anything else that expects single component values.  And you shouldn't output the color from a normal map directly into a normal input, or use a bump node without any height input, or use a bump node with a distance of 23.5 when your entire mesh is about 4 units tall.